1. Field of the Invention
The present invention relates to a ferroelectric thin film formation composition containing a metal compound to form a ferroelectric thin film, a ferroelectric thin film and a method of fabricating a ferroelectric thin film.
2. Description of the Related Art
A piezoelectric element having a ferroelectric thin film containing a crystal, which is typified by lead-zirconate-titanate (PZT) and the like, has spontaneous polarization, high dielectric constant, an electrooptic effect, a piezoelectric effect, a pyroelectric effect and the like. Thus, the piezoelectric element described above is applied to wide-ranging device development. Moreover, as a method of forming such a ferroelectric thin film, for example, a sputtering method, a sol-gel method, a CVD method and the like are known. Among the above-described methods, the sol-gel method is a method of forming a film by sequentially performing application, drying and calcination of a sol (colloidal solution). Accordingly, the sol-gel method has an advantage that the ferroelectric thin film can be easily formed at relatively low cost. For example, by use of the sol-gel method as described above, the ferroelectric thin film can be formed in the following manner. Specifically, a ferroelectric thin film formation composition (sol) is applied onto a substrate, the ferroelectric thin film formation composition being obtained by dissolving a metal compound such as a metal alkoxide in a solvent such as alcohol and adding an arbitrary additional agent, as the need arises, for adjustment. Thereafter, the sol is dried, degreased and calcined.
However, if the ferroelectric thin film is formed by use of a conventional ferroelectric thin film formation composition, a radially extending uneven striped pattern, that is, a striation occurs in the ferroelectric thin film. Thus, there is a problem that an even ferroelectric thin film cannot be formed. Note that the cause of occurrence of the striation has not been clearly elucidated in the present circumstances.
Accordingly, in order to solve the problem as described above, there has been proposed a ferroelectric thin film formation composition in which a water content in a sol composition is set to a predetermined amount or less (for example, see Japanese Patent Laid-Open No. 2001-48540). However, there is a problem that selection of the composition, for example, use of a compound containing water of crystallization or a compound such as alkoxide, which has a hydroxy group by hydrolysis, is significantly limited.
Moreover, there has been proposed a perovskite oxide thin film formation source solution containing silicon (for example, see Japanese Patent Laid-Open No. 2001-72416). This perovskite oxide thin film formation source solution is intended to eliminate the striation by containing silicon which has chemical stability that a composition of the source solution hardly reacts with organic matter and has very low surface tension.
However, as described above, silicon is chemically stable and never reacts with other compounds. Thus, even if silicon is dried or calcined, silicon remains as it is in the ferroelectric thin film as impurities. Consequently, there arises a problem that the impurities may adversely affect piezoelectric properties.